An “all-solid” microbattery is an electrochemical component enabling to store energy. Such batteries, having a total thickness smaller than 15 micrometers, have the specificity of having a solid electrolyte.
Generally, their structure comprises a stack of the following layers (FIG. 1):                a substrate;        a current collector for the cathode;        a cathode material;        a solid electrolyte material;        an anode material;        a current collector for the anode.        
The layers of materials may be formed by successive CVDs (chemical vapor depositions), possibly plasma-enhanced (PE-CVD), or by PVD (Physical Vapor Deposition), and particularly by cathode sputtering for the electrolyte.
In the case of all-solid microbatteries implying lithium ions, the latter transit between the anode and the cathode where oxidation-reduction reactions take place.
Such reactions imply an electron exchange according to an external circuit. Indeed, the electrolyte separating the cathode from the anode blocks the passage of electrons. Such an electron exchange thus enables to ensure the microbattery charge/discharge cycles.
Two types of lithium-based microbatteries may be distinguished:                lithium microbatteries, having their lithium ions originating from a metal lithium anode;        Li-ion microbatteries, having their lithium ions originating from a lithiated electrode material (cathode or anode).        
Li-ion batteries may be manufactured either in the charged state, or in the discharged state. In the first case, lithium is present in the anode layer at the time of the manufacturing, while it is present in the cathode layer in the second case.
The solid electrolyte may be formed by cathode sputtering deposition in a reactor generally having a so-called parallel planar geometry (FIG. 2). In this technique, a target material (8) having a chemical composition close to that desired for the electrolyte is attached to a metal support (cathode (9)) in a reactor or chamber (5). This cathode (9) is negatively biased by means of an electric generator. Under the effect of the electric field, the gas (N2 for example) present in the vicinity of the target (8) is ionized. The positive ions of the ionized gas bombard the target and expel atoms from the target. These atoms then deposit back on the surface opposite to where the object (14) to be covered, supported by an object-holder (13), is placed.
To avoid disturbing the growth of the deposit, nothing separates the target from the substrate to be covered with the electrolyte.
However, the deposition of a solid electrolyte on a previously-lithiated electrode may generate problems specifically linked to the technology of lithium accumulators.
Indeed, in a cathode sputtering deposition method, on deposition of the electrolyte layer on a lithiated electrode layer (FIG. 3a), the surface of the sample to be covered cannot drain off incident electrons (FIG. 3b). Accordingly, it charges negatively until it reaches a so-called floating potential in equilibrium with the potential of the plasma (FIG. 3b).
The presence of negative charges at the surface results in attracting the lithium present in the lithiated electrode. Thus, lithium diffuses through the growing electrolyte, towards the surface in contact with the plasma. Simultaneously, the electrons, created by the deinsertion of lithium ions Li+, are drained off from the lithiated electrode via the substrate holder (FIG. 3c). The lithium excess at the surface of the electrolyte is ejected back into the plasma (FIG. 3d). Such a “depletion” phenomenon impoverishes the lithium structure, and thus causes a decrease in the electrochemical performance.
The depletion phenomenon occurs during the solid electrolyte deposition. It depends:                on the lithiated materials of the electrode. Indeed, the higher the potential of the lithiated electrode relative to the metal lithium, the less the phenomenon will be marked. Accordingly, prior art microbatteries generally comprise a cathode made of lithiated cobalt oxide (LiCoO2) which has a lower potential than, particularly, a cathode based on LiV2O5, SiLi, GeLi, Li4Ti5O12, LiTiOS, LiTiS2.        on the diffusion speed of lithium within the lithiated electrode material. The faster lithium diffuses in the material, the faster the microbattery will discharge, possibly integrally before the electrolyte deposition.        on the geometry of the reactor having the electrolyte manufactured therein. Indeed, the floating potential acquired by a part plunged in a plasma chamber depends on the conditions of electric excitation of this plasma (pressure, power, nature of the gases . . . ), but also on the geometry of the deposition chamber.        on the architecture of the stack comprising the cathode/electrolyte/anode sequence. Prior art battery manufacturing methods may implement so-called “shadow mask” techniques on insulating substrates (polyamide, PEN, borosilicate, mica . . . ). Such methods enable to form a plurality of batteries of small dimensions (typically <10 cm2) simultaneously in a same deposition reactor. In such methods, the lithiated electrode having the electrolyte deposited thereon is electrically insulated from the rest of the deposition frame. Thus, the electrons released during the possible deinsertion of the lithium of the lithiated electrode remain confined within the latter, thus limiting the depletion process.        
The problem that the present invention aims at solving particularly relates to the forming of a solid lithium-based electrolyte layer while avoiding the depletion phenomenon, that is, the accumulation of negative charges at the surface of the sample during a solid electrolyte material deposition.